Optical objective



3 5 O -4 7 Z 5 Q Search R00" May 7 1945- A. cox 2,399,858 r OPTICAL OBJECTIVE Filed oct. 2. 1944 DI Sl .D3 0405 0 '0557 -0304 0537. -0304 4013 #070s 0l 5/ D2 S2 04 S3 05 om f 0990 0mm X Inventor 4 A liorne Patented May 7, 1946 Claims.

This invention relates to an optical objective, for photographic or other purposes, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortion, and comprising a double-concave divergent component disposed behind two convergent components and in front of another convergent components. It is to ybe understood that the side of the longer conjugate is herein regarded as the .front of the objective in accordance with the usual convention.

each consist of a simple element, but it has been proposed to make the convergent second component compound so that it consists of a double- V convex element cemented in front of a doubleconcave element. In one such arrangement, the cemented surface in the second component is utilised to provide diierential under-correction of red and blue light for the marginal rays, so as to make the objective substantially achromatic both for the axial and for the marginal rays. This involves giving the cemented surface relatively deep curvature with a small diierence (of the order of 0.02) between the mean refractive indices of the two elements cemented together. In another arrangement the cemented surface is used for a quite different purpose, namely, to obtain a. very high relative aperture of, say, F/1.5 without reducing the back focal length, the surface in this case being much sha1- lower and having a somewhat greater index difference, say between 0.025 and 0.045, across it. In both these arrangements the material of the double-convex element has higher index than that of the double-concave element.

The present invention again uses a second component consisting of a double-convex elementnf higher mean refractive index cemented in front to provide improved correction for oblique spherical aberration.

To this end according to the invention the mean refractive index of the material of the doubleconvex element in the second component exceeds that of the double-concave element cemented to it by at least 0.06, and the radius of curvature of the front surface of the simple divergent third component bears to that of the rear surface thereof a ratio between 1.0 and 2.0, the axial air separation between the second and third components lying between 0.04 and 0.085 times the equivalent focal length of the objective. The radius of curvature of the front surface of the front component preferably lies between 0.6 and 0.9 times the equivalent focal length of the objective, and that of the rear surface of the second component is preferably not greater than 0.6 times such focal length.

In such objective the four components usually' Search Room 2,399,858 UNITED STATES PATENT OFFICE OPTICAL OBJECTIVE Arthur Cox, Leicester,

Taylor, Taylor & Hobson Limited, Leicester, England, a company of Great Britain Application October 2, 1944, Serial No. 556,851 In Great Britain August 2, 1944 England, assigner to In the accompanying drawing,

Figures 1 and 2 respectively illustrate two convenient practical examples of objective according to the invention.

Numerical data for these two examples are given in the following tables, in which R'i, R2 represent the radii of curvature of the individual surfaces (the positive sign indicating that the Surface is convex to the front and the negative sign that it is concave thereto), D1. Dz represent the axial thicknesses of the lens elements, and Si, S2, S3 represent the axial air separations between the components. The tables also give the mean refractive index for the D-line and the Abb V number of the material used for each lens element. l

Example I Equivalent focal length 1.000. Relative aperture F/2.8

Thickness R efractive Abb V Radius. or iilpa' index nn number Di .0405 1. 6130 55. 7 lia-3.095

Si 0.0 Rz+.4403

Dz .0557 1. 644 48. 3 Iii-2.532

D: .0304 1.547 45. 7 Ri+.5364

Sa .0537 Ifo-.6011 l .D4 .0304 l. 652 33. 5 RVi-.4512

Si .1013 m+ao3s Dt .0706 1. 613 57. 6 Rv-.3972

. Example II Equivalent focal length 1.000. Relative aperture F/2.5

Thickness R etractlve .Abb V Radius gaap index nn number Di .0459 l. 6122 58. 7 12a-6.521

Si 0.0 Ra+.3984

D: .0214 1. 547 45. 8 Rei-.4407

Si .0745 R.5703 Di .0224 1. 621 36. 2 Rid-.4065

Ds .0612 1. 6132 55. 6 ltr-.4039

The back focal length in Example I is .8146 and in Example II is .7231 times the equivalent focal length of the objective. It will be noticed that the index difference across the cemented surface the radii Re and R1 is approximately 1.33 inv Example yI and 1.40 in Example II. These examples are both well-corrected for oblique spherical aberration as well as for the usual primary aberrations.

What I claim as my invention and desire to secure by Letters Patent is:

1. An optical objective corrected for spherical and chromatic aberrations, coma, astigmatism, eld curvature, distortion and oblique spherical aberration, and comprising four air-separated components, of which the first is a simple convergent component, the second a compound convergent component consisting of a double-convex convergent element cemented in front of a double-concave divergent element, the third a simple divergent component andthe fourth a simple convergent component, the front surface of the front component having a radius lying between 0.6 and 0.9 times the equivalent focal length of the objective, the mean refractive index of the material used for double-convex element of the second component exceeding that for the double-concave element cemented to it by at least 0.06, whilst the radius of curvature of the front surface of the divergent third component lies between 1.0 and 2.0 times that of the rear surface thereof. the axial air separation between the secondland third components lying between 0.04 and 0.085 times the equivalent focal length of the objective.

2. An optical objective corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature, distortionand oblique spherical aberration, and comprising four air-separated components, of which the'rst is a simple convergent component, the second a compound convergent component consisting of a double-convex convergent element cemented in front of a double-concave divergent element, the third a. simple divergent component and the fourth a simple convergent component, the rear surface of the second component having a radius of curvature not greater than 0.6 times the equivalent focal length of objective, the mean refractive index of the material used for the double-convex element of the second component exceeding that for the double-concave element cemented to it by at least 0.06, whilst the radius of curvature of the front surface of the divergent third component lies between 1.0 and 2.0 times that of the rear surface thereof, the axial air separation between the second and third components lying between 0.04 and. 0.085 times the equivalent focal length of the objective.

in which R1, Rz

3. An optical objective as claimed in claim 1 wherein the radius of curvature of the front surface of the front component is greater than that of the rear surface of the second component.

4. An optical objective having numerical data substantially as set forth in the following table:

Equivalent focal length 1.000.` Relative aperture F/2.8

Thickness Refractive Abb V Radius or ffilpa' index 1m number Dl .0405 1. 6130 55. 7 R13.095

Si 0.0 R14-.4403 D. .0561 1. 644 4s. a ffl-2.532

D: .0304 1. 547 45. 7 Rsi-.5364

Sa .0537 R41-.6011

Sx .1013 Rsi-3.038

D5 .0709 1. 613 57. 6 Riv-.3072

5. An optical objective having numerical data substantially as set forth in the following table:

Equivalent focal length 1.000. Relative aperture F/2.5

Thickness R traen Abb v Radius or air sepae ve ration index n number DI .0450 l. 6122 58. 7 lil-5.521

Si 0.0 RTI-.3984

lil-.9568

Dl .0214 1. 547 45. 8 12H-.4407

Si .0745 Ifo-.5703

Sa .0090 12H-Z266 D5 .0612 1. 0132 55. 6 Rt-.4039

curvature of the individual surfaces, the positive sign indicating that `the surface Vis convex to the front and the negative sign that it is concave thereto, D1, Dz represent the axial thicknesses of the lens elements, and Si, Sz. S: represent the axial airv separations between the components.

ARTHUR COX.

represent the radii of 

